(Project Leader: Craig Patrick Hunter) Intercellular RNA transport is a potentially important means of cell-cell communication. In the nematode C. elegans the RNA channel SID-1 is essenfial forthe cell-to-cell transport of silencing RNAs, SidTI and SidT2 (SidT1/2) are the highly conserved vertebrate homologs and published reports indicate that fish, mouse, and human versions of SidT1/2 have RNA transport acfivity. Analyses of RNA transport in cultured cells derived from SidT2 knockout mice confirm these reports and establish SidTI and SidT2 knockout mice and derived cultured cells as valuable tools for the identification and characterization of RNA signaling pathways in mammals. Extracellular RNAs are present in many body fluids and are being explored as disease indicators. How these RNAs are selected, transported, and whether they have a biological function is unknown. To address these issues the RNA transport activity of SidTI/2 will be exploited to selectively identify RNAs that are purposefully extracellular. These SidT1/2-dependent extracellular RNAs will be validated and then, to unambiguously establish the fact of intercellular RNA transport, their expression and transport will be rigorously examined. This analysis will be collaborative with consortium partners, whom have established powerful experimental systems to detect intercellular RNA transport. Irhportantly, the dependence of RNA mobility on SidTI/2 provides the means to disrupt their transport between cells, which will be important for deciphering the physiological and developmental of these mobile RNAs. Parallel to these discovery efforts, the RNA transport mechanism and the RNA features that permit or restrict RNA transport will be elucidated. These efforts will also be collaborative among the consortium partners. These findings will have bearings on how RNA transport is regulated and how the RNA transport pathway can be exploited to develop RNA-based therapies, including the safe and effective delivery of siRNAs.